1. Field of Invention
This invention relates to processes for low temperature catalytic oxidation of lower hydrocarbon feed to carboxylic acids and dehydrogenated product, particularly the conversion of ethane/ethylene to acetic acid or direct oxidation of ethane to vinyl acetate monomer over mixed metal oxide catalysts. The feed includes sulfur containing compound capable of producing oxides of sulfur. The process achieves a high yield of partial oxidation products.
2. Description of the Related Art
Numerous processes are known for catalytic oxidation of ethane to oxygenated or oxy-dehydrogenated products. For example, U.S. Pat. No. 3,970,697, European Patent 627,401, European Patent Application 480,594 and International Application WO 99/13980 describe catalysts and processes for the production of acetic acid from ethane and ethylene. U.S. Pat. Nos. 4,250,346, 4,524,236, 4,568,790, 4,596,787 and 4,899,003 describe catalysts and processes for oxydehydrogenation of ethane to ethylene. U.S. Pat. Nos. 4,370,492, 5,185,308, 4,902,823.and International Application WO 98/05620 describe catalysts and processes for the production of vinyl acetate from ethylene, acetic acid and oxygen. U.S. Pat. No. 4,339,355 describes catalysts and processes for the production of acrylic acid from acrolein. U.S. Pat. No. 4,148,757 describes catalysts for the ammoxidation of olefins to acrylonitrile and for the oxidation of olefins to acrolein and acrylic acid. In order to increase activity and product selectivity , most of the catalytic systems described in these disclosures include the addition of promoting metals to the catalysts rather than any process gas or co-feed as a promoter.
Oxidative dehydrogenation is a well known process for converting saturated or partially saturated organic compounds to corresponding compounds containing a greater degree of unsaturation. Yields of the reaction products are related to the type of the catalyst system and to the process conditions. Oxidative dehydrogenation processes utilizing sulfur oxide are described in U.S. Pat. Nos. 4,188,490 and 3,970,697. The catalysts used in the processes of U.S. Pat. Nos. 4,188,490 and 3,970,697 include palladium and gold on supports such as zinc oxide, alumina and silica; the catalyst is pre-treated with sulfur compound in moist air so that the concentration of sulfur-containing modifier is from about 0.05% to about 25% of the pre-treated, zinc oxide supported pallladium and gold catalyst composition.
In U.S. Pat. Nos. 2,867,677, 2,423,418 and 2,720,550, sulfur dioxide is added in alkane dehydrogenation reactions which are run at very high temperatures above 400.degree. C. to 700.degree. C. where total oxidation products become dominant. Consequently, the yields of the desired product are rather low. Moreover, organic sulfide compounds formed as by products are adsorbed on the surface of the catalysts and hinder the overall reaction.
Accordingly, it would be desirable to provide a low temperature method which can have a significant impact on the productivity of the required products without effecting the integrity of the mixed metal oxide catalysts.